1. Field of the Invention
The present invention relates to a developing apparatus, an image forming apparatus, and a process cartridge which use a two-component developer to develop an electrostatic latent image formed on an image bearing member by an electronic photograph method, an electrostatic recording method, or the like, and relates to an electronic photograph image forming apparatus to which the process cartridge can be removably attached.
Here, image forming apparatuses and electronic photograph image forming apparatuses include copying machines, printers (such as LED printers and laser beam printers), fax machines, and word processors.
The process cartridge is defined as a cartridge into which at least charging means, developing means, or cleaning means and an electro-photosensitive body are integrated so that the cartridge can removably be attached to an electronic photograph image forming apparatus or as a cartridge into which at least developing means and an electro-photosensitive body are integrated so that the cartridge can be removably attached to an electronic photograph image forming apparatus.
2. Related Background Art
Conventionally, the so-called two-component developing method has been used as a developer which visualizes an electrostatic latent image formed on an image bearing member using a two-component developer which contains a nonmagnetic toner and a magnetic carrier.
The two-component developing method agitates a two-component developer using a developer agitating and carrying member disposed in a developer container containing the developer to electrostatically charge the toner by friction and then conveys the toner to a developing sleeve as a developer bearing member having a fixed magnet roller inside. Also, the developer is conveyed while being carried on the developing sleeve and fed to an electrostatic latent image to develop it.
In order to meet increasing needs for color copies (or documents printed in color) or save space, to be even smaller, inexpensive developing apparatuses have been being used. Process cartridges are widely used into which an electro-photosensitive body and processing means acting on the body are integrated so that they can be removably attached to an image forming apparatus. Because such a process cartridge allows a user himself to maintain an image forming apparatus independently of a service technician, the operability of the apparatus significantly increases. Thus process cartridges of this type are used in many electronic photograph image forming apparatuses.
The above-described developing apparatus and process cartridge hold a small amount of developer because the developing apparatus is installed in a limited space around an image bearing body. Thus by separately providing a toner feeder (hereinafter called a xe2x80x9chopperxe2x80x9d), the developing apparatus is often adapted to feed only toner when the toner is consumed, reducing running cost.
FIG. 8 is a schematic sectional view of an example of a conventional developing apparatus. First and second agitating members 111 and 112 are disposed in a developer container 107, containing a two-component developer. In the figure, a hopper 114 which contains toner to be replenished is provided above the developer container 107. The hopper 114 is provided at its bottom with an opening, which is above the second agitating member 112. Near the opening, a toner feed member 116 is rotatably provided. In response to a signal from a toner sensor 113, that is, means for detecting the concentration of toner in developer, or toner amount detecting means, the toner feed member 116 rotates to feed toner from the hopper 114 to the developer container 107.
In response to a toner concentration detection signal from the toner sensor 113 in the developer container 107, the toner feed member 116 rotates to feed toner from the hopper 114. When the toner sensor 113 senses xe2x80x9ctoner is emptyxe2x80x9d which means that toner in the developer container 107 is below a predetermined level, the toner feed member 116 in the hopper 114 operates to replenish toner. Based on a value as detected when the toner sensor 113 senses xe2x80x9ctoner is empty (that toner in the developer container 107 is below the predetermined level), the amount of toner to be replenished is determined from a predetermined function.
After the toner is fed from the hopper 114 onto the second agitating member 112 in the developer container 107, the toner is replenished over the entire area along the length of the developer container 107 with the rotation of the second agitating member 112 and the first agitating member 111. The first and second agitating members 111 and 112, which are shaped like a screw propeller, can freely rotate in the directions indicated by arrows in the figure. The first and second agitating members 111 and 112 are also adapted to rotate in synchronism with a developing sleeve 104 or only when toner is fed.
Here, to form an image of a uniform density, it is essential to stably feed to the developing sleeve 104 a developer with a uniform concentration of toner to a photosensitive drum. It is preferably for stable feeding such a developer that toner is agitated immediately after it is replenished.
A method is known which conveys developer in the direction of the axis of the developing sleeve 104 to agitate the developer, using an agitating member, adapted by forming a spiral blade around a rotating shaft to enhance agitation performance. Another method is also known which agitates and conveys developer, using flat ribs extending divergently from a shaft to further enhance agitation performance.
However, it is difficult for the conventional developing apparatus and process cartridge to always satisfactorily agitate and convey a two-component developer, containing toner and a carrier, well irrespective of environmental changes and durability operation, resulting in a defect of a final image, such as an uneven density.
An uneven density of an image can be caused by insufficient agitation power of an agitating member. That is, it takes much time for toner fed from the hopper 114 to uniformly diffuse into the carrier, and thus developer is fed to the developing sleeve 104 before an even toner concentration is reached, resulting in an uneven image density.
Moreover, such insufficient agitation causes the toner sensor 113, developer amount detecting means, to malfunction. That is, because insufficiently agitated developer leaves a carrier and toner separated from each other, the toner sensor 113 continues to sense xe2x80x9ctoner is emptyxe2x80x9d and requires replenishment of toner.
It is an object of the present invention to provide a developing apparatus and an image forming apparatus which can produce a high-quality image stably.
It is another object of the present invention to provide a developing apparatus and an image forming apparatus which can agitate a two-component developer thoroughly in a short time, feed a developer with an even toner concentration to a developer bearing body, and stably form a high-quality image free from defects at any time.
It is still another object of the present invention to provide a developing apparatus and an image forming apparatus which can thoroughly agitate a two-component developer in a short time and prevent developer amount detecting means from malfunctioning.
It is a further object of the present invention to provide a developing apparatus, including: a developer container which holds a two-component developer containing magnetic particles and toner; a developer agitating and conveying member which is provided in the developer container to agitate and convey developer; and a toner feed port for feeding toner to the developer container, wherein an area is formed where the developer agitating and conveying member is partly exposed out of developer in the direction of developer conveyance by the developer agitating and conveying member, and toner is fed through the toner feed port to the area.
It is a still further object of the present invention to provide an image forming apparatus, including: an image bearing body which bears a latent image; a developing apparatus which develops a latent image formed on the image bearing body, the developing apparatus including: a developer container which holds a two-component developer containing magnetic particles and a carrier; a developer agitating and conveying member which is provided in the developer container to agitate and convey developer; and a toner feed port for feeding toner to the developer container.
These and other objects, features, and advantages of the present invention will be understood more clearly by reading the following detailed description with reference to the drawings.